Oswald Theodore Avery (1877-1955), US molecular biologist. Avery was born in Canada, but was educated in New York. He is most famous for the part he played in the research known as the Avery-MacLeod-McCarty experiment in the early 1940s. This work demonstrated that DNA (deoxyribonucleic acid) was the transforming principle in the bacterial extracts that could cause benign bacterial strains to turn into the more virulent strains. Although Avery and his fellow researchers did not receive a Nobel Prize, this is considered one of the fundamental discoveries in genetics. Photographed in the 1930s.